<template>
  <ul class="list">
    <li class="item" v-for="item of letters" :key="item" 
    @touchstart="handleTouchStart"
    @touchmove="handleTouchMove" 
    @touchend="handleTouchEnd" 
    @click="handleLetterClick" 
    :ref="item"> {{item}} </li>
  </ul>
</template>

<script>
  export default {
    name: 'CityAlphabet',
    data() {
      return {
        touchStatus: false,
        startY: 0
      }
    },
    updated() {
      this.startY = this.$refs['A'][0].offsetTop
    },
    computed: {
      letters(){
        const letters = [];
        for(let i in this.cities){
          letters.push(i);
        }
        return letters;
      }
    },
    props: {
      cities: Object
    },
    methods: {
      handleLetterClick(e){
        this.$emit('change', e.target.innerText);
      },
      handleTouchStart(){
        this.touchStatus = true
      },
      handleTouchMove(e){
        if(this.touchStatus){
          if(this.timer){
            clearTimeout(this.timer)
          }
          this.timer = setTimeout(() => {
            const startY = this.$refs['A'][0].offsetTop
            const touchY = e.touches[0].clientY - 79
            const index = Math.floor((touchY - startY) /17.9)+1
            if(index >= 0 && index < this.letters.length){
              this.$emit('change', this.letters[index])
            }
          },16)
          

        }
      },
      handleTouchEnd(){
        this.touchStatus = false

      }
    },
  }
</script>

<style lang="stylus" scoped>
  @import '~styles/varibles.styl';
  .list{
    display flex
    flex-direction column
    justify-content center
    position absolute
    text-align center 
    top 1.58rem
    bottom 0
    right 0
    width .4rem
    // background red
    .item{
      line-height .36rem
      color $bgColor
    }
  }
</style>